Can Nico be a girl's name?

I have a friend that's a girl and her name is Nico. I know a girl whose name is Sean (pronounced Shaun). I mean, I like both of those names on girls and I'm used to the fact that they are girly-ish girls with guy names. They are sisters, but I'm mainly focusing on Nico. Her name isn't Nicole. Her mom showed me her birth certificate and it says "Nico Angela Thornton". I found it weird that her mom showed me that though